1. Field of the Invention
The present invention relates to a rotation-sensored rotary connector comprising: a rotary connector for electrically connecting an electrical component installed on a steering to a vehicle-body side; and a rotation sensor for detecting a rotational angle of the steering.
2. Description of the Prior Art
Included in a conventional type of rotary connector is a structure in which a projection protruded from a rotor of a rotary connector is fitted to a steering, to thereby transmit the driving torque of the steering to the rotor of the rotary connector.
JP-A-11-329649 (329649/1999) describes the above-mentioned constitution which further includes a rotation sensor mounted on the rotary connector to thereby unitize them so as to detect a steering angle of the steering by the rotation sensor. FIG. 1 is a schematic cross-sectional view of such a constitution in which the rotor 51 of the rotary connector 50 is mounted to the steering W of a steering shaft S, and the rotation sensor 60 includes a rotor 61 coupled to the rotor 51 via looseness compensating spring (not shown in FIG. 1). Namely, the rotor 61 of the rotation sensor 60 is mounted on the rotor 51 of the rotary connector 50, to thereby transmit the driving torque of the steering W to the rotor 61 of the rotation sensor 60. The rotation sensor 60 further includes a stator 62, and the rotor 61 and stator 62 are provided with sensing members, respectively, so as to detect the rotational angle of the rotor 61 of the rotation sensor 60 as the rotor 61 rotates.
Relatedly, outputs of rotation sensors are exemplarily used as a piece of information of vehicle stability control for stabilizing behavior of a vehicle during running, or used to adjust an oil pressure of a power steering, thereby requiring a strict precision. Thus, outputs of rotation sensors have to be measured precisely.
However, in the above-mentioned constitution, it is likely that the rotational angle can not be detected precisely, because of accumulation of misalignment between the steering shaft S as a measuring target and the rotation sensor 60, including looseness (i.e., play) between the steering shaft S and steering wheel W, and including relative angle deviation between the rotors of the rotary connector 50 and rotation sensor 60 such as due to the looseness compensating spring.
There will be described hereinafter the reason why larger detection errors are caused particularly when the output of the rotation sensor 60 is detected through the rotary connector 50.
The output signal of the rotation sensor 60 has precision which is affected by the looseness between the rotor 61 and stator 62 of the rotation sensor 60. Namely, if the relative positions of the rotor 61 and stator 62 are changed by the looseness therebetween, the output signal is correspondingly changed of course.
It is thus preferable that the relative positions of the rotor 61 and stator 62 of the rotation sensor 60 are always kept unchanged so as to obtain outputs with higher precision, such that the clearance between the rotor 61 and stator 62 is exemplarily restricted to an extremely small value of ±0.2 mm to obtain satisfactory characteristics for products.
Meanwhile, because the required precision of the rotary connector 50 is not so strict as the rotation sensor 60, the rotor 51 of the rotary connector 50 coupled to the steering W has a clearance between the coupling portion of the rotor 51 of the rotary connector 50 and the coupling portion of the steering W which clearance is usually larger than that between the rotor 61 and stator 62 of the rotation sensor 60, and such a larger clearance is generally on the order of ±0.5 mm (which is 2.5 times that for the rotation sensor). Conversely, if no clearance were provided between these coupling portions, the dimensional precision of those members constituting the coupling portions of the steering shaft S and steering W and of the steering W and rotary connector 50 should be set extremely strictly. Even if the members could be machined with such a strict dimensional precision, assembling is made difficult in turn. It is, thus, inevitable to provide a duly larger clearance between the coupling portion of the rotor 51 of the rotary connector 50 and the coupling portion of the steering W.
Therefore, the rotor 61 of the rotation sensor 60 is displaced by an amount corresponding to the above-mentioned looseness concerning the rotary connector 50, in case that the steering angle of the steering W is detected by the rotation sensor 60 through the rotor 51 of the rotary connector 50. Thus, the output signal of the rotation sensor 60 is fluctuated by an amount corresponding to the looseness, thereby failing to detect a steering angle with an excellent precision.
There will be described hereinafter further defects to be caused when the rotation sensor 60 detects the rotational angle of the steering W through the rotary connector 50.
As described above, the clearance between the rotor 61 and stator 62 of the rotation sensor 60 is on the order of ±0.2 mm. Since the stator 62 of the rotation sensor 60 is mounted on a combination switch bracket via cushioning member, the stator 62 is allowed to move by a certain amount correspondingly to the looseness of the rotor 61 of the rotation sensor 60 relative to the stator. However, the looseness compensating capability of the stator 62 of the rotation sensor 60 is occasionally exceeded, such as when the rotor 61 of the rotation sensor 60 is largely moved due to the clearance between the rotor 51 of the rotary connector 50 and the steering W. In such a situation, the rotor 61 of the rotation sensor 60 may impose an excessive side pressure onto the stator 62 to thereby increase the rotational torque of the rotor 61, and in the worst case, the rotor 61 is prevented from rotating to thereby possibly disable the rotational angle detection.
Moreover, the rotor 51 of the rotary connector 50 is generally integrated with a canceling cam (not shown in FIG. 1) for operating a canceling mechanism for blinkers. The canceling cam is to rotate while striking against the canceling mechanism, when the canceling mechanism is to operated. Thus, vibrations upon striking the canceling mechanism in the conventional constitution are inevitably transmitted to the rotor 61 of the rotation sensor 60 through the rotor 51 of the rotary connector 50 because the rotor 61 is coupled to only the rotor 51, thereby possibly affecting the output signal of the rotation sensor 60.